Image processing apparatus and image processing method

ABSTRACT

A CPU ( 201 ) updates scene data ( 206 ) by changing the management order of the data of virtual objects in the scene data ( 206 ) based on the processing result of a search of the scene data ( 206 ), which is executed upon generating an image of virtual space viewed from a first viewpoint. The CPU ( 201 ) sets the updated scene data ( 206 ) as scene data ( 206 ) to be used to generate an image viewed from a second viewpoint different from the first viewpoint.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a virtual space image generationtechnique.

2. Description of the Related Art

As the processing capability of computers has improved recently, studiesof a Virtual Reality technique of providing real experiences to usershave progressed (see non-patent reference 1). The technique isimplemented by expressing virtual space by computer graphics anddisplaying it on an HMD (Head Mounted Display) or a wall-type display.

In this field, an element necessary for providing a high-qualityexperience to a user is the speed of image generation. The processingspeed required for generating a virtual space image while following auser's viewpoint movement is generally supposed to be 10 to 15frames/sec. To meet this requirement, a technique of generating an imageat a high speed while maintaining expressive power higher than beforehas been developed.

The recent sophisticated computer parallelization and virtual spacehandling techniques have enabled a real-time ray tracing method whichwas impossible previously (see non-patent reference 2). The ray tracingmethod disclosed in non-patent reference 2 is particularly calledreal-time ray tracing and has extensively been studied. This techniqueallows expressions of reflection and refraction, high-speed shadowgeneration, and expressions of global illumination, which were difficultfor a conventional rasterization method. It is therefore possible togenerate a high-quality image.

As the expressive power of image generation processing rises, acalculation load necessary for obtaining a high-quality image isincreasing steadily. The amount of data to be processed is alsoincreasing to meet the desires for displaying objects in virtual spacein real time. For these reasons, even when real-time ray tracing isimplemented, a calculation load reducing technique is indispensable tooutput at a high frame rate while maintaining high expressive power.

Patent reference 1 discloses a method of increasing the efficiency ofanimation generation by ray tracing using a time-series correlation. Ananimation expresses a motion by updating the screen (frame) that changesgradually. The gradually changing screen contains a time-seriescorrelation (coherence) such as the positional relationship of objectsthat should be within sight.

In image generation processing using ray tracing, generally, the timerequired for a search in ray tracing is the longest. In patent reference1, using the coherence between time-series images, the result of apreceding frame is reused for a portion where no change occurs betweenthe preceding frame and the current frame, thereby shortening the searchtime in the ray tracing method.

-   [Non-patent reference 1] “VR World Construction Technique”,    supervised by Susumu Tachi, and edited by Michitaka Hirose,    Baifukan, 2000-   [Non-patent reference 2] Ingo Wald, Carsten Benthin, Markus Wagner,    and Philipp Slusallek, “Interactive Rendering with Coherent    Ray-Tracing” in Computer Graphics Forum/Proceedings of the    EUROGRAPHICS 2001, pp. 153-164, 20 (3), Manchester, United Kingdom,    Sep. 3-7, 2001-   [Patent reference 1] Japanese Patent No. 2532055

The above method increases the time-series efficiency and speed of imagegeneration processing by ray tracing. However, processing of generatinga plurality of images of different viewpoints at once is not taken intoconsideration at all. For example, to make a user wearing an HMDexperience virtual space, it is necessary to generate two images forright and left eyes simultaneously and present them to him/her as astereoscopic image. In stereoscopic image generation, the right-eyeimage and left-eye image are generated based on different viewpointpositions and orientations, and therefore, the ray reflection directionsare different. For this reason, the time-series correlation cannot beused. To generate a stereoscopic image to be presented to the user,image generation processing must be executed for each of the right andleft eyes.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of theabove-described problem, and has as its object to provide a technique ofefficiently generating a plurality of virtual space images.

According to the first aspect of the present invention, an imageprocessing apparatus for rendering a common object from a plurality ofviewpoints, comprises:

a first unit which renders a first image; and

a second unit which renders a second image,

wherein each of the first unit and the second unit renders an unrenderedregion by referring to information obtained by a process of rendering ofthe other unit.

According to the second aspect of the present invention, an imageprocessing method executed by an image processing apparatus forrendering a common object from a plurality of viewpoints, comprises:

a first step of rendering a first image; and

a second step of rendering a second image,

wherein in each of the first step and the second step, an unrenderedregion is rendered by referring to information obtained by a process ofrendering in the other step.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining the outline of image processingaccording to the first embodiment of the present invention;

FIG. 2 is a block diagram showing the hardware configuration of acomputer applicable to an image processing apparatus according to thefirst embodiment of the present invention;

FIG. 3 is a flowchart illustrating processing executed by a computerhaving the configuration shown in FIG. 2 to generate virtual spaceimages to be presented to the right and left eyes of a user;

FIG. 4 is a view for explaining a ray tracing method and division ofvirtual space;

FIG. 5 is a view showing an example of the structure of a treerepresented by scene data 206;

FIG. 6 is a view showing a scene tree search;

FIG. 7 is a view for explaining the outline of image processingaccording to the second embodiment of the present invention;

FIG. 8 is a view for explaining the outline of image processingaccording to the second embodiment of the present invention;

FIG. 9 is a flowchart illustrating processing executed by a computerhaving the configuration shown in FIG. 2 to generate virtual spaceimages to be presented to the right and left eyes of a user according tothe second embodiment of the present invention;

FIGS. 10A and 10B are views for explaining processing of adaptivelydividing a screen;

FIG. 11 is a view for explaining image generation processing accordingto the third embodiment of the present invention;

FIG. 12 is a flowchart illustrating processing executed by a computerhaving the configuration shown in FIG. 2 to generate virtual spaceimages to be presented to the right and left eyes of a user according tothe fourth embodiment of the present invention;

FIG. 13 is a view for explaining the sequence of image generationprocessing by general rasterization;

FIG. 14 is a view for explaining a three-dimensional coordinateestimation method by stereoscopic vision;

FIG. 15 is a view for explaining the outline of image processingaccording to the fifth embodiment of the present invention; and

FIG. 16 is a flowchart illustrating processing executed by a computerhaving the configuration shown in FIG. 2 to generate virtual spaceimages to be presented to the right and left eyes of a user according tothe fifth embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings. The embodiments willbe explained as examples of preferred arrangements of the presentinvention described in the claims, but the present invention is notlimited to the embodiments to be described below.

First Embodiment

This embodiment assumes that virtual space images to be presented to theright and left eyes of a user (observer) are generated by a ray tracingmethod. More specifically, in this embodiment, a virtual space image tobe presented to one eye is generated, and the calculation resultobtained by the generation processing is stored. Then, the calculationresult is used to generate a virtual space image to be presented to theother eye. This increases the efficiency and speed of processing ofgenerating virtual space images to be presented to the eyes.

FIG. 1 is a view for explaining the outline of image processingaccording to this embodiment. This embodiment assumes that when a useris to experience virtual space, virtual space images of differentviewpoint positions and orientations are generated for the right andleft eyes by a ray tracing method. Hence, virtual space images based ondifferent viewpoint positions and orientations are respectivelydisplayed on a screen 101 for displaying an image to be presented to theuser's left eye and a screen 102 for displaying an image to be presentedto the user's right eye.

The viewpoint positions and orientations of the images displayed on thescreens 101 and 102 are assumed to be not so largely different, like theinterocular distance of a human. For this reason, in this embodiment,virtual objects displayed on the screen 101 are assumed to be seen onthe screen 102, too. Such assumption makes it possible to use thecalculation result obtained by generating the virtual space image forthe left eye even in the processing of generating the virtual spaceimage for the right eye.

An image processing apparatus 103 generates virtual space images to bedisplayed on the screens 101 and 102 by a ray tracing method.

Regions 104 of the screens 101 and 102 do not overlap in the visualfields of the right and left eyes. For the regions 104, the calculationresult obtained upon generating a virtual space image to be displayed ona screen cannot be reused. Hence, calculation is necessary in everyimage generation processing.

In image processing calculation using the ray tracing method, processingof searching for a virtual object that intersects a ray takes thelongest processing time.

The difficulty of a search depends on the abundance of virtual objects,i.e., the complexity of the scene. Assume that 10,000 virtual objectsexist in a scene. If the 10000th object in a scene tree which managesthe elements included in the virtual space using a tree structure is therendering target, the search processing needs to be performed 10,000times every time a virtual space image of a frame is generated (thevirtual object search processing will be described later in detail).

In this embodiment, when a virtual object to be seen to one eye wassearched from scene data in order to generate a virtual space image tobe presented to the eye, the search result is used in processing ofgenerating a virtual space image to be presented to the other eye. Thisreduces the total calculation load and speeds up image generationprocessing.

FIG. 2 is a block diagram showing the hardware configuration of acomputer applicable to the image processing apparatus according to thisembodiment. The hardware of a computer is not limited to the illustratedconfiguration. A computer having any other configuration is also usableif it mainly includes an execution unit which executes processing and astorage unit which stores programs and data.

In FIG. 2, using computer programs and data stored in a RAM 202 and aROM 203, a CPU 201 controls the overall computer and executes eachprocessing to be described later as the processing of the computer.

The RAM 202 has an area for temporarily storing a processing program 205(computer program) and scene data 206 loaded from an external storagedevice 204 and also has a work area to be used by the CPU 201 to executevarious kinds of processing. That is, the RAM 202 can provide variouskinds of areas, as needed.

The ROM 203 stores a boot program and setting data of the computer.

The external storage device 204 is a mass information storage devicerepresented by a hard disk drive. The external storage device 204 storesthe processing program 205 and the scene data 206 as well as an OS(Operating System). The external storage device 204 also stores knowninformation to be described later and information to be used by thoseskilled in the art in a practical manner in the following description.The computer programs and data stored in the external storage device 204are loaded to the RAM 202, as needed, under the control of the CPU 201.The CPU 201 executes various kinds of processing using the loadedcomputer programs and data.

The processing program 205 stored in the external storage device 204 isa computer program which causes the CPU 201 to execute various kinds ofprocessing to be described later as the processing of the computer.

The scene data 206 is data to manage elements included in virtual spaceby a tree format (tree structure). For example, when a virtual objectincludes known polygons, the scene data 206 contains the color data andnormal vector data of the polygons and the coordinate value data of eachvertex of the polygons (these data will be referred to as geometricinformation hereinafter). If the virtual object has texture mapping, thescene data 206 also contains texture mapping data. The scene data 206also contains information of the type and luminance of a virtual lightsource which irradiates the virtual space.

When a virtual space image is rendered using a ray tracing method, thescene data 206 also contains space division information for facilitatingintersection determination of a ray and a virtual object. In thisembodiment, a virtual space image is generated by a ray tracing method,as described above.

An input device 207 inputs the position and orientation information ofeach of the right and left eyes of the user who observes a virtual spaceimage. Hence, various devices are applicable as the input device 207.

For example, a keyboard or a mouse may be used as the input device 207.In this case, the user manually inputs the position and orientationinformation of each eye using the input device 207.

A position and orientation sensor may be used as the input device 207.In this case, the position and orientation sensor is attached to theuser's head. The position and orientation sensor inputs the measurementresult to the RAM 202 as data. The CPU 201 obtains the positions andorientations of the right and left eyes using the measurement resultdata, the position and orientation relationship between the position andorientation sensor and the right eye, and that between the position andorientation sensor and the left eye.

As described above, various methods are available to acquire theposition and orientation information of the user's right and left eyes,and the present invention is not limited to one method. The device to beapplied as the input device 207 is determined in accordance with themethod.

A display device 208 displays the virtual space image for the right eyeand that for the left eye generated by the CPU 201 and is formed from,e.g., a CRT or a liquid crystal panel. The display device 208 can alsodisplay any other information, as a matter of course. More specifically,the display device 208 can display the processing result of the CPU 201using an image or a text.

A bus 209 connects the above-described units.

Processing executed by a computer having the configuration shown in FIG.2 to generate virtual space images (right eye virtual space image andleft eye virtual space image) to be presented to the right and left eyesof the user will be described next with reference to FIG. 3 that is aflowchart illustrating the processing.

Note that the computer programs (including the processing program 205)and data (including the scene data 206) to make the CPU 201 execute theprocessing according to the flowchart shown in FIG. 3 are stored in theexternal storage device 204. As described above, the computer programsand data are loaded to the RAM 202, as needed, under the control of theCPU 201. The CPU 201 executes processing using the loaded computerprograms and data. Hence, the computer executes the processing accordingto the flowchart shown in FIG. 3.

In step S300, initialization processing is executed for subsequentprocessing. The initialization processing includes processing of readingout the processing program 205 from the external storage device 204 andloading it to the RAM 202. The initialization processing also includesprocessing of allocating an area to be used for subsequent processing inthe RAM 202.

In step S301, the scene data 206 is read out from the external storagedevice 204 and sequentially expanded on the RAM 202. The data expandedon the RAM 202 at this time contains a scene tree and node information,which describe the tree structure of the overall scene. The nodeinformation contains the geometric information and material informationof virtual objects which are individual elements of the scene tree, andvirtual light source information.

In step S302, the position and orientation information of each ofviewpoints (right and left eyes) in virtual space is acquired in the RAM202. The acquisition can be done by various methods, as described above.In this embodiment, the user manually inputs the information using theinput device 207. However, predetermined fixed values may be used as theviewpoint position and orientation information of the right eye and thatof the left eye.

In step S303, a virtual space image (first screen) to be presented toone eye (first viewpoint) is generated using the data group acquired inthe RAM 202 in step S301 and the position and orientation information ofthe right and left eyes acquired in the RAM 202 in step S302. Thegenerated first screen is displayed on the display screen of the displaydevice 208. The processing in this step will be described later indetail.

In step S304, a virtual space image (second screen) to be presented tothe other eye (second viewpoint) is generated using the scene data 206updated in the processing in step S303. The generated second screen isdisplayed on the display screen of the display device 208. Theprocessing in this step will also be described later in detail.

In step S305, it is determined whether to finish the processing. Tofinish the processing, for example, the user inputs an end instructionusing the input device 207. Alternatively, a processing end conditionmay be set in advance. If it is determined to finish the processing, theprocessing is ended. If the processing is not to be ended, the processreturns to step S302 to perform the processing of generating the righteye virtual space image and left eye virtual space image of the nextframe.

The ray tracing method will be described next with reference to FIG. 4.FIG. 4 is a view for explaining the ray tracing method and division ofvirtual space.

In the ray tracing method, processing of projecting a ray from aviewpoint 401 set in virtual space to each pixel of a virtual screen 402is executed. The intersection between each ray that has passed throughthe virtual screen 402 and a virtual object in, e.g., octree-dividedvirtual space 403 is determined. When a ray intersects the virtualobject, the information of the virtual object is searched for from thescene data 206. Reflection of light from a virtual light source 405 withrespect to the virtual object, which is represented by the foundinformation, is calculated, thereby determining the pixel value on thevirtual screen 402. This processing is done for all pixels of thevirtual screen 402.

The virtual space 403 is octree-divided to facilitate the determinationof intersection between a ray and the virtual object. For the raytracing method, many techniques of facilitating intersectiondetermination by dividing space have been proposed. Examples are kd-treedivision and BVH (Boundary Volume Hierarchy). This embodiment does notdepend on the space division algorithm. Hence, any space division methodis usable.

The information of the virtual object that intersects a ray is obtainedby searching for a scene tree in the scene data 206.

The scene data 206 will be described next. FIG. 5 is a view showing anexample of the structure of a tree represented by the scene data 206.

“World” 501 is a node corresponding to the base (root) node of a scene(virtual space). This node defines the absolute coordinates of thescene.

“Camera” 502 is a node which stores the position and orientation, andthe angle of view of the viewpoint.

“Object” 503 is a node which holds various kinds of information of thevirtual object. Generally, since a scene includes a plurality of virtualobjects, “Sub-object” 505 which groups the virtual objects in the sceneis prepared under the “Object” 503.

“Transform” 506 is a parameter that defines the position and orientationof the “Object” 503 with respect to the absolute coordinates of the“World” 501.

The “Sub-object” 505 is a node which groups “object 1” 507, “object 2”,. . . which are minimum units representing a virtual object. Objectnodes as many as the virtual objects that appear in the scene areassociated under the “Sub-object” 505.

The “object 1” 507 has the information of “shape” 508, “material” 509,and “transform” 510.

The “shape” 508 has geometric shape information such as the coordinatevalue data of each vertex of polygons of the “object 1” 507 and thenormal vector data.

The “material” 509 stores, as attribute data, the texture information ofthe “object 1” 507 and diffused reflection information and mirrorreflection information of light from the light source.

The “transform” 510 represents the position and orientation informationof the “object 1” 507.

“Light” 504 has the information of a virtual light source thatirradiates the virtual space scene and stores the data of the position(geometric information), type (e.g., direct light, point source, or spotlight), and luminance information (including tint information) of thevirtual light source.

In the above-described arrangement, to obtain the information of avirtual object that intersects a ray, processing of searching for ascene tree (a search in the scene data) shown in FIG. 5 needs to beperformed as many as the number of intersections of rays. That is, theamount of search processing becomes enormous when a ray intersects avirtual object at a deep position of the hierarchical structure or in ascene including many virtual objects.

A scene tree search in the scene data 206 will be described next. FIG. 6is a view showing a scene tree search.

A scene tree 601 is a scene tree in the initial state. Each of childnodes 602 in the scene tree 601 represents a virtual object seen from agiven viewpoint (viewpoint of interest). A search route 603 represents aroute to search for a node of a virtual object (child node 602) when aray intersects it. The route is preset.

In the processing of generating a virtual space image seen from aviewpoint of interest, conventionally, the child nodes 602 are searchedalong the search route 603 as many as the pixels of virtual objectscorresponding to the child nodes 602 on the display panel. In the scenetree 601, since the child nodes 602 are located at the end of the searchroute 603, every search is time-consuming. In this embodiment, toshorten the time, the positions of the child nodes 602 are moved to thetop portion of the search route 603, thereby updating the scene tree601.

More specifically, when the child nodes 602 are found, creation of a newscene tree is started in the RAM 202. First, a copy of the scene tree601 is created in the RAM 202. The position of each child node 602 inthe copied scene tree is moved to the top portion of the search route603, thereby updating the copied scene tree. That is, the scene data isupdated by changing the management order of the data of the virtualobject in it. In FIG. 6, reference numeral 604 denotes a copied scenetree that is updated by moving the positions of the child nodes 602 tothe top position of the search route 603. As indicated by 605, the routeof searching for the child nodes 602 is shorter than the search route603. The arrangement order (management order) of the nodes in the childnodes 602 is not particularly limited.

When the processing of generating a virtual space image seen from theviewpoint of interest is ended, the scene tree 601 is updated to thecopied scene tree. The updated scene tree 601 is set as a scene tree tobe used to generate a virtual space image seen from the other viewpointexcept the viewpoint of interest.

As described above, the scene tree updated in the process of generatinga virtual space image for a given viewpoint is used to generate avirtual space image for the next viewpoint. Hence, when generatingvirtual space images for a plurality of viewpoints, the search distancebecomes shorter for a viewpoint located later in the generation order.

A node that has not been searched for in the process of generating avirtual space image is arranged at the endmost position of the new scenetree (search route 603). Even a non-searched node is copied to the newscene tree. For this reason, no problem is posed even when the first andsecond screens have different virtual objects in the visual field. Thatis, a virtual object that exists only in the second screen is not thetarget of rearrangement in the new scene tree. However, since the newscene tree stores the information of the virtual object, the virtualobject can be displayed without any problem.

As described above, when generating a virtual space image for oneviewpoint, the position of the node of a virtual object to be searchedin the scene tree is rearranged at the top position of the search route,thereby implementing efficient search processing.

In the node rearrangement operation for new scene tree creation, thefrequency of search may be counted, and the scene tree may be rearrangednot based on the search order but in the order of search frequency. Morespecifically, the number of times of search is counted for each node.When the generation processing of one virtual space image is ended, thenodes are arranged from the top of the search route in descending orderof count value.

Additionally, if no virtual object is in the visual field in the processof image generation of the first screen, the scene tree searchprocessing is unnecessary in the second screen. Hence, when informationrepresenting that no virtual object is in the visual field is added tothe information of the new scene tree in the process of image processingof the first screen, it is possible to execute the second screen imagegeneration processing at a high speed.

For the second screen image generation processing when no virtual objectis in the visual field of the first screen, a background image isprepared as a texture in advance, and image generation processing isperformed not by ray tracing but by texture rendering.

In some cases, a virtual object is included only in the second screen.In this case, the presence/absence information of the virtual objectcannot be used. However, the phenomenon that only one eye can see avirtual object occurs when the disparity is high because of theextremely short distance between the virtual object and the viewpointposition. To use the presence/absence information of a virtual object, arestriction is imposed to make a virtual object exist at a predetermineddepth value or more from the viewpoint so as to prevent the disparityfrom becoming high. This restriction makes it possible to use thepresence/absence information of a virtual object.

If the viewpoint position and orientation in first screen imagegeneration are the same or almost the same as those in second screenimage generation, the search result of the first screen equals that ofthe second screen. This allows to reuse the search result of the firstscreen for the second screen image generation processing.

The problem of scene search is always necessary in various kinds ofimage generation processing (e.g., rasterization method, volumerendering method, and particle rendering method). Hence, the method ofincreasing the efficiency of image generation by scene reconstruction iseffective even when the image generation processing is changed. Hence,this embodiment is applicable to various kinds of image generationprocessing in general.

In this embodiment, the display device 208 of the computer displays thefirst and second screens. However, any other display device may displaythe first and second screens. For example, when an HMD is connected tothe computer, the right eye display screen of the HMD may display theright eye virtual space image while the left eye display screen maydisplay the left eye virtual space image.

Second Embodiment

In the first embodiment, the first and second screens are generated bysequential processing. In the second embodiment, however, the first andsecond screens are divided and generated in parallel.

FIG. 7 is a view for explaining the outline of image processingaccording to this embodiment.

This embodiment assumes that each of the first and second screens isdivided into upper and lower regions, and each region is processed byone CPU.

Referring to FIG. 7, reference numeral 701 denotes an upper region(partial region) of the first screen; and 703, a lower region of thefirst screen. The upper region 701 and lower region 703 are obtained bydividing the first screen into upper and lower parts. The upper andlower regions do not overlap.

Referring to FIG. 7, reference numeral 702 denotes an upper region ofthe second screen; and 704, a lower region of the second screen. Theupper region 702 and lower region 704 are obtained by dividing thesecond screen into upper and lower parts. The upper and lower regions donot overlap.

In this embodiment, the upper region of one screen and the lower regionof the other screen are generated in parallel. In the generationprocessing of the upper region of one screen, original scene data iscopied, and the copied scene tree is updated, as in the firstembodiment, to move the nodes of a virtual object that appears in theupper region of one screen to the top of the search route. In thegeneration processing of the lower region of the other screen, originalscene data is copied, and the copied scene tree is updated, as in thefirst embodiment, to move the nodes of a virtual object that appears inthe lower region of the other screen to the top of the search route.That is, in this embodiment, the scene data for one screen (first scenedata) and the scene data for the other screen (second scene data) aregenerated.

Next, the lower region of one screen and the upper region of the otherscreen are generated in parallel. In the generation processing of thelower region of one screen, the scene data updated in the process ofgenerating the lower region of the other screen is used. In thegeneration processing of the upper region of the other screen, the scenedata updated in the process of generating the upper region of one screenis used.

As described above, two processes are executed in parallel. Hence, scenetree search processing can be started efficiently when image generationhas finished up to the half of a screen.

FIG. 8 is a view for explaining the outline of image processingaccording to this embodiment. The same reference numerals as in FIG. 1denote the same parts in FIG. 8, and a description thereof will not berepeated. In this embodiment, to generate a first screen 101 and asecond screen 102 in parallel, a screen region division control unit 801is added. This allows to divide each screen into regions and executeimage generation processing in first and second halves in generating theimages of the first screen 101 and second screen 102 in parallel.

Additionally, in this embodiment, information exchange is performed inthe second half of image generation. Hence, information acquired in theprocess of image generation of the second screen 102 is also output toan image processing apparatus 103 and used for image generation of thefirst screen 101, unlike the first embodiment.

Processing according to this embodiment, which is executed by a computerhaving the configuration shown in FIG. 2 to generate virtual spaceimages to be presented to the right and left eyes of the user, will bedescribed next with reference to FIG. 9 that is a flowchart illustratingthe processing.

Note that the computer programs (including a processing program 205) anddata (including scene data 206) to make a CPU 201 execute the processingaccording to the flowchart shown in FIG. 9 are stored in an externalstorage device 204. As described above, the computer programs and dataare loaded to a RAM 202, as needed, under the control of the CPU 201.The CPU 201 executes processing using the loaded computer programs anddata. Hence, the computer executes the processing according to theflowchart shown in FIG. 9.

In step S900, initialization processing is executed for subsequentprocessing. The initialization processing includes processing of readingout the processing program 205 from the external storage device 204 andloading it to the RAM 202. The initialization processing also includesprocessing of allocating an area to be used for subsequent processing inthe RAM 202.

In step S901, the scene data 206 is read out from the external storagedevice 204 and sequentially expanded on the RAM 202. The data expandedon the RAM 202 at this time contains a scene tree and node information,which describe the tree structure of the overall scene. The nodeinformation contains the geometric information and material informationof virtual objects which are individual elements of the scene tree, andvirtual light source information.

In step S902, each of the screen for the right eye and the screen forthe left eye is divided into two, upper and lower regions. Regioninformation representing each divided region is generated and stored inthe RAM 202. The region information contains, e.g., informationrepresenting to which screen (right eye screen or left eye screen) theregion belongs, and the coordinate positions of the upper left and lowerright corners of the region.

In step S903, the position and orientation information of each ofviewpoints (right and left eyes) in virtual space is acquired in the RAM202. The acquisition of the pieces of position and orientationinformation can be done by various methods, as described above. In thisembodiment, the user manually inputs the information using the inputdevice 207. However, predetermined fixed values may be used as theposition and orientation information of the right eye and that of theleft eye.

In step S904, the upper region of a virtual space image (first screen)to be presented to one eye is generated using the data group acquired inthe RAM 202 in steps S901 and S902 and the position and orientationinformation of the right and left eyes acquired in the RAM 202 in stepS903. The generated upper region of the first screen is displayed on thedisplay screen of the display device 208.

Processing in step S905 is executed in parallel to step S904. In stepS905, the lower region of a virtual space image (second screen) to bepresented to the other eye is generated using the data group acquired inthe RAM 202 in steps S901 and S902 and the position and orientationinformation of the right and left eyes acquired in the RAM 202 in stepS903. The generated lower region of the second screen is displayed onthe display screen of the display device 208.

In step S907, the lower region of the first screen is generated usingthe scene data updated in step S905. The generated lower region of thefirst screen is displayed on the display screen of the display device208.

In step S908 parallel to step S907, the upper region of the secondscreen is generated using the scene data updated in step S904. Thegenerated upper region of the second screen is displayed on the displayscreen of the display device 208.

In step S909, it is determined whether to finish the processing. Tofinish the processing, for example, the user inputs an end instructionusing the input device 207. Alternatively, a processing end conditionmay be set in advance. If it is determined to finish the processing, theprocessing is ended. If the processing is not to be ended, the processreturns to step S903 to perform the processing of generating the righteye virtual space image and left eye virtual space image of the nextframe. And then, subsequent processing is performed for the next frame.

This embodiment assumes that the image generation of the first screenand image generation of the second screen are performed simultaneouslyin two processes by setting the parallel count to 2. However, theparallel count need not always be 2. The embodiment can also cope with aparallel count of 3 or more. In this case, a screen region is divided inaccordance with the parallel count, and a scene tree for increasing thesearch efficiency is generated in each process.

This embodiment assumes that image generation processing is executed bydividing a screen into two, upper and lower regions. However, a screenneed not always be divided into two, upper and lower regions. A screenmay be divided into two, left and right regions. When the parallel countincreases, the screen region division method may be changed accordingly.A preferably screen division method can be selected in accordance with asystem to be built or a scene to be experienced. At any rate, in thisembodiment, image generation is performed a plurality of number of timesto parallelly generate a virtual space image for one viewpoint and thatfor the other viewpoint.

<Modification>

An example of adaptive screen division will be described here.

FIGS. 10A and 10B are views for explaining processing of adaptivelydividing a screen.

Referring to FIG. 10A, image generation processing in the first screen101 starts from a position 1001 of the upper left corner. Imagegeneration processing in the second screen 102 starts from a position1004 of the lower right corner. As shown in FIG. 10B, when the positionsof pixels that are currently being processed have reached the sameposition in the two screens, scene data updated upon generating thesecond screen is used for the first screen to process the remainingregion. For the second screen, scene data updated upon generating thefirst screen is used. In FIG. 10B, reference numeral 1002 denotes aprocessed region when the positions of pixels that are currently beingprocessed have reached the same position in the two screens.

As described above, according to this embodiment, a screen is divided inaccordance with the parallel processing capability of image generationprocessing to divisionally execute image generation processing. Thisallows to efficiently execute image generation processing at a highspeed.

Third Embodiment

In the first and second embodiments, image generation is donesequentially for each pixel. The third embodiment is largely differentfrom these embodiments in that only partial regions undergo imagegeneration in the first half of image generation processing, scene datais updated, and then, image generation processing is executed again morespecifically.

FIG. 11 is a view for explaining image generation processing accordingto this embodiment. A virtual space image (screen) 1104 included in thevisual field from a viewpoint corresponds to the first or second screen.Specific regions 1101 are set in the image 1104. In FIG. 11, thespecific regions 1101 are set discretely at an equal interval. In thisembodiment, each specific region 1101 corresponds to one pixel of theimage 1104. However, the size of the specific region 1101 is notparticularly limited. In addition, the specific regions need not alwayshave the illustrated layout.

In this embodiment, one virtual space image is generated in two steps.In generation of the first step (first generation), images in thespecific regions are generated. In generation of the second step (secondgeneration), images in the remaining regions (regions except for thespecific regions 1101) are generated using scene data updated in thefirst generation in the same way as in the first embodiment.

In this embodiment, regions to which rays are projected are setdiscretely as described above. This makes it possible to reconstruct thescene data of the entire scene at a high speed without calculating allpixels on the screen.

For the regions except for the specific regions 1101, image generationcan be performed efficiently by executing detailed image generationprocessing again after scene reconstruction. The method of thisembodiment is very effective mainly for image generation processing suchas ray tracing which calculates each pixel in determining a pixel valueon the screen.

The scene reconstruction in the specific regions may be applied to botha first screen 101 and a second screen 102. Alternatively, a resultobtained by applying the scene reconstruction to one of the screens maybe applied to image generation processing in both of the first andsecond screens.

Fourth Embodiment

In the first, second, and third embodiments, processing of efficientlygenerating images by exchanging scene data output in each imagegeneration process has been described. The fourth embodiment isdifferent from these embodiments in that in image generation processingby rasterization, viewpoint coordinate transformation is executed forthe depth value output in an image generation process for each of theleft and right eyes and the processed depth value is used.

The outline of image processing according to this embodiment is the sameas that described in the second embodiment in many points, and onlydifferent points will be described.

In this embodiment, first, the luminance values of partial regions,which do not overlap, of an upper region 701 and a lower region 704obtained by region division as shown in FIG. 7 are calculated by anormal rendering method. The depth values (the values of the Z buffer)obtained in the process of calculating the luminance value at this time,and the material information of the target object are stored in a RAM202.

The depth values stored in the RAM 202 are transformed into depth valuesin the coordinate system of the other viewpoint. If the depth valuesobtained by the transformation and the material information of thetarget object are available, the luminance value can be calculated.

Processing according to this embodiment, which is executed by a computerhaving the configuration shown in FIG. 2 to generate virtual spaceimages to be presented to the right and left eyes of the user, will bedescribed next with reference to FIG. 12 that is a flowchartillustrating the processing. The same step numbers as in FIG. 9 denotethe steps of executing the same processes in FIG. 12.

In steps S904 and S905, processing of obtaining the luminance value ofeach pixel of each divided region is performed, in addition to theprocessing described in the second embodiment.

In step-S1201, the depth values (the values of the Z buffer) obtained inthe processing in steps S904 and S905, the normal information of eachvertex of the target object, and the material information of the targetobject are stored in the RAM 202.

In step S1202, viewpoint coordinate transformation is performed for thedepth values stored in the RAM 202 in step S1201. The coordinatetransformation is processing of transforming the depth value for theleft eye into the depth value for the right eye and transforming thedepth value for the right eye into the depth value for the left eye.

Finally in steps S907 and S908, processing of calculating the luminancevalue of each pixel of each divided region based on the materialinformation stored in step S1201 is performed for the depth valuestransformed in step S1202, in addition to the processing described inthe second embodiment.

A luminance value determination method in the rendering processing ofthis embodiment will be described next.

FIG. 13 is a view for explaining the sequence of image generationprocessing by general rasterization.

In modeling transformation 1301, the information (three-dimensionalcoordinates) of scene data stored in an external storage device 204 isloaded to the RAM 202 and transformed into world coordinates. That is,in modeling transformation 1301, a virtual object is rotated anddeformed in three-dimensional space. This transformation also includesbasic coordinate transformation such as enlargement/reduction androtation on local object space. The data obtained upon processing of themodeling transformation 1301 do not depend on the viewpoint position andorientation. Hence, the right and left eyes can share the data.

In viewpoint transformation 1302, the position and orientation of avirtual object defined on the world coordinates are transformed into aposition and orientation on the local coordinate system based on theposition and orientation of a virtual camera. More specifically, amatrix for viewpoint transformation is obtained in advance, andviewpoint transformation is done using a matrix operation for eachvertex of the virtual object. As a result, the originalthree-dimensional scene is transformed into a scene on the coordinatesystem viewed from the virtual camera.

Data obtained upon processing of the viewpoint transformation 1302depend on the respective viewpoints. Hence, the right and left eyescannot share the data.

In projection transformation 1303, transformation from thethree-dimensional coordinate system defined by the virtual camera to atwo-dimensional coordinate system is done. By the projectiontransformation 1303, the virtual space is mapped as two-dimensionalinformation on a plane (virtual screen) viewed from the virtual camera.

In rasterization 1304, after clipping processing and hidden surfaceremoval are executed, the luminance value of each pixel of thetwo-dimensional image of the scene projected onto the virtual screen iscalculated.

In the clipping processing, the polygons of the virtual object outsidethe visual field are discarded, and only polygons in the visual fieldare cut out. In the hidden surface removal, polygons which are notdirected to the viewpoint, i.e., polygons which are theoreticallyinvisible from the viewpoint are discarded. At this time, polygons whichshould be visible from the viewpoint are written in the Z buffer indescending order of the distance to the viewpoint. When the values aresequentially overwritten, a depth value corresponding to each pixelvalue is calculated, and only polygons visible from the viewpoint areselected.

In the rasterization 1304, after the hidden surface removal, the normalinformation of each vertex and the material information of the virtualobject are extracted from the scene data for shading processing. Textureinformation is also extracted, as needed. If the left and right eyes seethe same object, it is possible to share the material information of theobject. Reflected light is calculated based on the extracted data andthe position and orientation information of the virtual viewpoint. Then,the luminance value of each pixel on the virtual screen is calculated.However, the result of shading processing calculated from the materialinformation of the object changes depending on the position andorientation of the viewpoint and therefore cannot be shared.

In display 1305, the pixels which are colored finally are displayed on amonitor or another display device.

When a common virtual object is observed from different viewpoints inthe general rasterization processing, the data obtained by the modelingtransformation 1301 and the material information of the object can beshared without transformation processing. However, the depth valuesobtained in the process of the rasterization 1304 can also be used byviewpoint coordinate transformation. However, occlusion may occurdepending on the positional relationship between the viewpoint and theobject, and it may be impossible to accurately calculate the depthvalues. In this case, each luminance value is determined by referring tothe corresponding pixel value of the preceding frame.

The method of calculating the luminance value of each pixel from thedepth values obtained by viewpoint coordinate transformation will bedescribed next.

FIG. 14 is a view for explaining a three-dimensional coordinateestimation method by stereoscopic vision.

As shown in FIG. 14, an xyz absolute coordinate system 1401 is definedin three-dimensional space. The left and right camera lenses arearranged so that the absolute coordinates of their centers are set to0_(L)=(0,0,0) and 0_(R)=(d,0,0) which are spaced apart by a distance d.Let f be the focal length of the lens, i.e., the distance from the lenscenter to each of the left and right image planes. A virtual object 1402is observed from thus set virtual viewpoints. A right eye screen and aleft eye screen on which the observed images are projected are definedas virtual screens 1403R and 1403L, respectively.

When the right eye observes a point P on the virtual object 1402, thepoint P is projected to a point P_(R)(x_(R),y_(R)) on the virtual screen1403R. When the left eye observes the point P on the virtual object1402, the point P is projected to a point P_(L)(x_(L),y_(L)) on thevirtual screen 1403L. The coordinates of the points P_(L) and P_(R) arerelative coordinates based on origins set as the centers of the virtualscreens 1403L and 1403R, respectively.

At this time, a point P(x_(p),y_(p),z_(p)) on the surface of the targetobject can be obtained by triangulation using a triangle formed from ameasuring point and the centers of the two cameras.

If the points P_(L) and P_(R) and various parameters are known, thethree-dimensional coordinates of a target can be calculated. This is thegeneral depth estimation method using stereoscopic vision in computervision.

In this embodiment, when a pixel value on the screen for one of the leftand right eyes and the three-dimensional coordinates of a targetcorresponding to the pixel are known, the pixel value of a correspondingpixel on the screen for the other eye is determined using the depthestimation method based on stereoscopic vision. For example, when thepoint P_(R)(x_(R),y_(R)) and the point P(x_(p),y_(p),z_(p)) on thesurface of the target object are given as inputs, the pointP_(L)(x_(L),y_(L)) is calculated.

Hence, if the viewpoint position and orientation are known, and thepoint P on the surface of the target object could be calculated using adepth value obtained by viewpoint coordinate transformation, it ispossible to calculate corresponding points on the virtual screens.

In steps S907 and S908, processing of loading the material informationof the object, which is stored in the RAM 202, in correspondence withthe point on the virtual screen obtained by calculation is performed, inaddition to the processing described in the second embodiment. Shadingprocessing and texture mapping processing are executed by the processingof rasterization 1304, thereby calculating individual luminance values.This processing is repeated until all pixels are calculated. The imagegeneration method by rasterization is a known technique which isimplemented using hardware for performing general graphics processing.

In the above-described processing, information obtained by the processof calculating the luminance value of a divided region on one screen isshared, thereby calculating the luminance value of the correspondingregion on the other screen.

Fifth Embodiment

In the first to fourth embodiments, processing of efficiently generatingimages by exchanging information obtained in the image generationprocess when generating a stereoscopic image has been described. Thefifth embodiment assumes image generation using a camera system for twoor more eyes and is different from the above embodiments in that ascreen region is divided into two or more regions, and image generationprocessing is applied to each region.

FIG. 15 is a view for explaining the outline of image processingaccording to this embodiment.

Rendering results for three viewpoints are displayed on a first screen1501, second screen 1502, and third screen 1503, respectively. In thisembodiment, each screen is divided into three regions, and rendering isperformed in each region.

Regions 1504 to 1506 are rendering regions where processing starts firstin the respective screens. In this embodiment, the regions 1504 to 1506are set not to overlap. When rendering has finished in the regions 1504to 1506 of the screens, calculation for uncalculated regions 1507 to1509 starts by referring to the calculation results of the regions 1504to 1506. When calculation for the uncalculated regions 1507 to 1509 hasfinished, calculation for the remaining regions is performed.

Processing according to this embodiment, which is executed by a computerhaving the configuration shown in FIG. 2 to generate virtual spaceimages to be presented to three eyes, will be described next withreference to FIG. 16 that is a flowchart illustrating the processing.The same step numbers as in FIG. 9 denote the steps of executing thesame processes in FIG. 16.

In step S902, each of the three screens (first screen, second screen,and third screen) is divided into three, upper, middle, and lower stages(corresponding to the number of cameras). The division form is notparticularly limited. Each screen may be divided vertically into equalparts. Alternatively, the divided regions may be changeable depending onthe complexity of the scene.

In step S1601 a, rendering processing of the upper stage of the firstscreen is performed. In step S1601 b, rendering processing of the middlestage of the second screen is performed. In step S1601 c, renderingprocessing of the lower stage of the third screen is performed. Therendering processing in each of steps S1601 a, S1601 b, and S1601 c isexecuted in the same way as in the other embodiments.

In step S1602, the rendering results in steps S1601 a, S1601 b, andS1601 c are stored in a RAM 202.

In step S1603 a, the luminance value in the region of the middle stageof the first screen is determined by referring to the rendering resultof the upper stage of the first screen, which is stored in the RAM 202,and rendering processing of the middle stage is executed. In step S1603b, the luminance value in the region of the lower stage of the secondscreen is determined by referring to the rendering result of the middlestage of the second screen, which is stored in the RAM 202, andrendering processing of the lower stage is executed. In step S1603 c,the luminance value in the region of the upper stage of the third screenis determined by referring to the rendering result of the lower stage ofthe third screen, which is stored in the RAM 202, and renderingprocessing of the upper stage is executed. However, the regions whererendering is performed in steps S1603 a, S1603 b, and S1603 c can bearbitrary regions which need only be uncalculated regions at the time ofcalculation.

In step S1604 a, the luminance value in the region of the lower stage ofthe first screen is determined by referring to the rendering result ofthe middle stage of the first screen, and rendering processing of thelower stage is executed. In step S1604 b, the luminance value in theregion of the upper stage of the second screen is determined byreferring to the rendering result of the lower stage of the secondscreen, and rendering processing of the upper stage is executed. In stepS1604 c, the luminance value in the region of the middle stage of thethird screen is determined by referring to the rendering result of theupper stage of the third screen, and rendering processing of the middlestage is executed.

In this embodiment, the calculation results in steps S1603 a, S1603 b,and S1603 c are not stored in the RAM 202. However, depending on thebuilt system, the pieces of information stored in step S1602 may beoverwritten by the pieces of information calculated in steps S1603 a,S1603 b, and S1603 c.

Assume that the viewpoints are arranged in the horizontal direction, andthe results obtained by arranging the screens corresponding to theviewpoints in accordance with the arrangement order of the viewpointsare the first screen, second screen, and third screen. In this case, theimage of the first screen can be generated more efficiently by using therendering processing result of the second screen with the closerviewpoint than by using the result of the third screen. Hence, to referto obtained information, a suitable means can be selected depending onthe built system.

As described above, even when two or more virtual viewpoints are used toobserve a common virtual object, it is possible to efficiently executerendering at a high speed by dividing each screen into an arbitrarynumber of regions and sharing the calculation results of the respectiveregions.

Sixth Embodiment

In region division, the efficiency can be maximized when no regionsoverlap between the first screen and the second screen. However, if theregions do not overlap at all, the edges of boundary portions becomenoticeable. The edges can be made unnoticeable by providing an overlapregion of several pixels near each boundary edge, and compositing andsmoothing images obtained by calculation. The size of the overlap regionupon region division can be determined by employing a suitable meansdepending on the built system.

Other Embodiments

The object of the present invention is also achieved by the followingmethod. A recording medium (or storage medium) which records softwareprogram codes to implement the functions of the above-describedembodiments is supplied to a system or apparatus. The storage medium isa computer-readable storage medium, as a matter of course. The computer(or CPU or MPU) of the system or apparatus reads out and executes theprogram codes stored in the recording medium. In this case, the programcodes read out from the recording medium themselves implement thefunctions of the above-described embodiments. The recording medium thatrecords the program codes constitutes the present invention.

The computer executes the readout program codes, and the operatingsystem (OS) running on the computer partially or wholly executes actualprocessing on the basis of the instructions of the program codes,thereby implementing the functions of the above-described embodiments.

Assume that the program codes read out from the recording medium arewritten in the memory of a function expansion card inserted to thecomputer or a function expansion unit connected to the computer. The CPUof the function expansion card or function expansion unit partially orwholly executes actual processing on the basis of the instructions ofthe program codes, thereby implementing the functions of theabove-described embodiments.

The recording medium to which the present invention is applied storesprogram codes corresponding to the above-described flowcharts.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2007-273088 filed Oct. 19, 2007 and Japanese Patent Application No.2008-185295 filed Jul. 16, 2008 which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. An image processing apparatus for rendering acommon object which can be viewed from a plurality of viewpoints,comprising: a management unit which manages a plurality of virtualobjects; a dividing unit which divides a first screen image of a firstviewpoint into a first half and a second half regions and divides asecond screen image of a second viewpoint into a first half and a secondhalf regions, where the first half and the second half regions of thesecond screen image correspond those of the first screen image,respectively; a first determination unit which determines whether avirtual object can be viewed from the first viewpoint in the first halfregion of the first screen image, one by one in a first order for thefirst viewpoint among the plurality of virtual objects and determineswhether a virtual object can be viewed from the second viewpoint in thesecond half region of the second screen image, one by one in a firstorder for the second view point among the plurality of virtual objects;a first rendering unit which renders the first half region of the firstscreen image viewed from the first viewpoint based on data of thevirtual object which can be viewed from the first viewpoint and rendersthe second half region of the second screen image viewed from the secondviewpoint based on data of the virtual object which can be viewed fromthe second viewpoint, in parallel; an update unit which updates thefirst order for the first viewpoint and the first order for the secondviewpoint of the plurality of virtual objects to a second order for thefirst viewpoint and a second order for the second viewpoint,respectively, by arranging the virtual object which can be viewed fromthe first viewpoint in the first half region of the first screen imageat a high order position in the second order for the second viewpointand the virtual object which cannot be viewed from the first viewpointat the lowest order position in the second order for the secondviewpoint and arranging the virtual object which can be viewed from thesecond viewpoint in the second half region of the second screen image ata high order position in the second order for the second viewpoint andthe virtual object which cannot be viewed from the first viewpoint atthe lowest order position in the second order for the second viewpoint;a second determination unit which determines whether a virtual objectcan be viewed from the first viewpoint in the second half region of thefirst screen image, one by one in the second order for the firstviewpoint among the plurality of virtual objects and determines whethera virtual object can be viewed from the second viewpoint in the firsthalf region of the second screen image, one by one in the second orderfor the second viewpoint among the plurality of virtual objects; and asecond rendering unit which renders the second half region of the firstscreen image viewed from the first viewpoint based on data of thevirtual object which can be viewed from the first viewpoint and rendersthe first half region of the second screen image viewed from the secondviewpoint based on data of the virtual object which can be viewed fromthe second viewpoint, in parallel.
 2. The apparatus according to claim1, wherein said update unit updates the first order to the second orderso that the virtual object which can be viewed from the viewpoint is inthe top of the second order.
 3. The apparatus according to claim 1,wherein said update unit updates the first order to the second order ina order of search frequency.
 4. The apparatus according to claim 1,wherein: said dividing unit sets a plurality of regions in the firsthalf region of the first screen image of the first viewpoint, said firstdetermination unit determines whether a virtual object can be viewedfrom the first viewpoint in each of the set regions in the first halfregion of the first screen image, one by one in the first order for thefirst viewpoint among the plurality of virtual objects, said firstrendering unit renders the plurality of regions in the first half regionof the first screen image viewed from the first viewpoint based on dataof the virtual object which can be viewed from the first viewpoint, saidupdate unit updates the first order for the first viewpoint by arrangingthe virtual object which can be viewed from the first viewpoint in theplurality of regions in the first half region of the first screen imageat a high order position in the updated first order of the firstviewpoint, and said first determination unit determines whether avirtual object can be viewed from the first viewpoint in a region exceptthe plurality of regions in the first half region of the first screenimage, one by one in the updated first order for the first viewpointamong the plurality of virtual objects, said first rendering unitrenders the region except the plurality of regions in the first halfregion of the first screen image viewed from the first viewpoint basedon data of the virtual object which can be viewed from the firstviewpoint.
 5. The apparatus according to claim 1, wherein each of saidfirst rendering unit and said second rendering unit performs renderingby transforming a depth value obtained by the process of rendering intoa coordinate system from the viewpoint.
 6. The apparatus according toclaim 1, wherein the first viewpoint corresponds to one eye of anobserver, and the second viewpoint corresponds to the another eye of theobserver.
 7. The apparatus according to claim 1, wherein the managementunit manages a plurality of data items including geometric shapeinformation of the virtual object in a virtual space and materialinformation of the virtual object, and the update unit updates the firstorder of the plurality of data items including the geometric shapeinformation and the material information of the virtual object to thesecond order.
 8. A non-transitory computer-readable storage medium whichstores a program for causing a computer to function as each unitincluded in an image processing apparatus of claim
 1. 9. The apparatusaccording to claim 1, wherein the rendering information indicates theinfluence for pixels by a source of light, which influence is obtainedby a ray-tracing process.
 10. An image processing method executed by animage processing apparatus for rendering a common object which can beviewed from a plurality of viewpoints, comprising: dividing a firstscreen image of a first viewpoint into a first half and a second halfregions and dividing a second screen image of a second viewpoint into afirst half and a second half regions, where the first half and thesecond half regions of the second screen image correspond to those ofthe first screen image, respectively; a first determination step ofdetermining whether a virtual object be viewed from the first viewpointin the first half region of the first screen image, one by one in afirst order for the first viewpoint among the plurality of virtualobjects and determining whether a virtual object can be viewed from thesecond viewpoint in the second half region of the second screen image,one by one in a first order for the second view point among theplurality of virtual objects; a first rendering step of rendering thefirst half region of the first screen image viewed from the firstviewpoint based on data of the virtual object which can be viewed fromthe first viewpoint and rendering the second half region of the secondscreen image viewed from the second viewpoint based on data of thevirtual object which can be viewed from the second viewpoint, inparallel; an updating step of updating the first order for the firstviewpoint and the first order for the second viewpoint of the pluralityof virtual objects to a second order for the first viewpoint and asecond order for the second viewpoint, respectively, by arranging thevirtual object which can be viewed from the first viewpoint in the firsthalf region of the first screen image at a high order position in thesecond order for the second viewpoint and the virtual object whichcannot be viewed from the first viewpoint at the lowest order positionin the second order for the second viewpoint and arranging the virtualobject which can be viewed from the second viewpoint in the second halfregion of the second screen image at a high order position in the secondorder for the second viewpoint and the virtual object which cannot beviewed from the first viewpoint at the lowest order position in thesecond order for the second viewpoint; a second determination step ofdetermining whether a virtual object can be viewed from the firstviewpoint in the second half region of the first screen image, one byone in the second order for the first viewpoint among the plurality ofvirtual objects and determining whether a virtual object can be viewedfrom the second viewpoint in the first half region of the second screenimage, one by one in the second order for the second viewpoint among theplurality of virtual objects; and a second rendering step of renderingthe second half region of the first screen image viewed from the firstviewpoint based on data of the virtual object which can be viewed fromthe first viewpoint and rendering the first half region of the secondscreen image viewed from the second viewpoint based on data of thevirtual object which can be viewed from the second viewpoint, inparallel.